1. Field of the Invention
This invention relates to a record confirmation apparatus, and more particularly to a record confirmation apparatus suitably applicable to a recording-reproducing apparatus using a disc-like record bearing member such as an optical disc.
2. Description of the Prior Art
In an information recording-reproducing apparatus, the following systems are known as a system for recording information on a record bearing member such as an optical disc and judging whether the information has been accurately recorded. A first system is such that as soon as a writing signal is stored in a memory, the writing signal is recorded on a track of the record bearing member, whereafter the same track is scanned to read out the recorded information and this read-out signal is compared with the writing signal stored in the memory, thereby judging whether the information has been accurately recorded. In this system, however, a memory of huge capacity is necessary and there is an inconvenience that much time is required for the confirmation of the record because the same track is scanned twice. There is also known a system in which, to decrease the storage capacity of the memory, the above-desscribed operation is effected for each of of several sectors into which a track is divided, but again in this system, it is necessary to scan the same track as frequently as double the number of sectors and therefore, much time has been required for the confirmation of the record.
Also, in an information recording-reproducing apparatus which has recording means and reproducing means discretely, there is a record confirmation apparatus as shown in FIGS. 1 and 2 of the accompanying drawings. In FIG. 1, reference numeral 1 designates a record bearing member such as an optical disc, and reference numerals 2, 3 and 4 denote recording tracks, of which the outermost track is designated by 2. Reference numeral 5 designates an optical head, reference numeral 6 denotes a writing beam spot, reference numeral 7 designates a reading-out beam spot, and reference numeral 8 indicates the direction of rotation of the record bearing member 1. .theta. is the angle formed by the writing beam spot 6 and the reading-out beam spot 7 with respect to the center of the record bearing member when the optical head 5 lies on the outermost track 2. At this time, the reading-out beam spot 7 is spaced apart from the writing beam spot 6 by an amount corresponding to (m+1/2) bits. In FIG. 2, reference numeral 9 designates a clock generator, reference numeral 10 denotes an m-bit shift register, reference numeral 11 designates an exclusive OR gate, reference numeral 12 denotes an inverter, and reference numeral 13 designates a JK flip-flop. The m-bit shift register 10, the exclusive OR gate 11, the inverter 12 and the JK flip-flop 13 together constitute comparing means.
Operation will now be described. FIG. 3 is a timing chart. The writing signal S.sub.6 is latched in the m-bit shift register 10 by the falling of a first clock signal CL with a time delay of 1/2 bit. Accordingly, the writing signal S.sub.6 is put out to S.sub.6 ' of (m+1/2) bits after it has been recorded on the record bearing member. At this time, the reading-out beam spot 7 reads the information S.sub.7 (2) before (m+1/2) bits of time as previously described. When the information is accurately recorded, the output of the exclusive OR gate 11 to which S.sub.6 ' and S.sub.7 (2) are input becomes LOW and the J terminal of the JK flip-flop 13 assumes HIGH and the K terminal of the JK flip-flop 13 assumes LOW, and this flip-flop 13 is latched by the rising of the first clock signal CL and the output Q thereof becomes HIGH. Also, when the information is not accurately recorded on the record bearing member, the output Q becomes LOW.
However, when the recording frequency and the angular speed of the record bearing member 1 are constant, the number of bits existing between the writing beam spo 6 and the reading-out beam spot 7 becomes greater as the optical head 5 moves to the inner track and thus, a bit delay is created in the read-out signal S.sub.7. That is, when the optical head 5 lies on the track 3 and where the information is accurately recorded on the record bearing member, signals input to the exclusive OR gate 11 are S.sub.6 ' and S.sub.7 (3) and, in this case, the output Q(3) becomes HIGH, but when the optical head 5 lies on the track 4 in which the output signal S.sub.7 (4) is delayed relative to the writing signal S.sub.6 by (m+1) bits, even where the information is accurately recorded on the record bearing member, the output Q(4) becomes LOW and the confirmation of the record becomes impossible. This has led to an inconvenience that the width of the track area which can be recorded on the record bearing member becomes very narrow.